All about Big Dipper: The only constellation within a constellation
Every time you look at the night sky, doesn’t the endless array of shining stars leave you wondering about how tiny we all are? We are all aware that stars like to huddle together in groups that astronomers call constellations. Our galaxy, Milky Way, is full of such constellations that leave us spellbound. One of them is the Big Dipper. But did you know that it is a rule breaker? Read on if you want to know more.
Interstellar for real
Big Dipper is a constellation within a constellation in our galaxy, and the only one of this kind! This well-established configuration of stars is often easy to recognise. However, truth be told, Big Dipper is not a constellation. Rather, it’s an asterism, an unofficial constellation with a small group of stars that form a visible pattern. It consists of the seven of the brightest stars of the constellation Ursa Major, also called the Great Bear. Big Dipper is known by different names in different cultures. For instance, it is known as Plough in England, Great Wagon in the rest of Europe, and Saptarishi in India (after the seven ancient holy sages).
Stars of the Big Dipper
Big Dipper is a collection of seven bright stars in the Ursa Major constellation, namely: Alkaid, Mizar, Alioth, Megrez, Phecda, Dubhe and Merak. While the first three form the handle, the rest four form the bowl. The brightest star among these seven is Alioth, which also happens to be the brightest star in Ursa Major. All the stars are approximately 80 light years away from Earth.
Apart from Dubhe and Alkaid, both of which move independently, the other stars move in a group of five and originated at the same time from a single cloud of gas and dust (nebula). They rotate as a family and are together known as Ursa Major Moving Group or Collinder 285.
Big Dipper is also unique as it contains the only twin stars, Mizar and Alcor, together called “The Horse and the Rider.” They are held together by gravity and are therefore called binary stars.
Position of the Big Dipper
Big Dipper is positioned in such a way that three of its stars comprise its handle-like feature, while the other four comprise its bowl-like structure. Together, they represent the tail and hindquarters of Ursa Major, respectively.
The Big Dipper is situated near the northern celestial pole (very close to the North Star). In the northern hemisphere, it is located at an angle of 41 degrees latitudinally, meaning that it can’t sink below the horizon during night-time.
Although the Big Dipper is visible all the year-round in the northern hemisphere, its position keeps on shifting. During springtime, it rises higher in the north-eastern part of the sky, and during autumn, it falls lower in the north-western part of the sky. Its orientation also changes because of its anticlockwise rotation, depending upon the seasons. In spring, it is usually upside down, while in summer it appears to be hanging by its handle. In contrast, it is close to the horizon and right side up during autumn and hangs by the bowl during winter. Mysterious, isn’t it?